The present invention relates to a composite plastic lens made of two thin lenses with their optical centers axes being such that the resultant optical center axis of the composite lens is at a predetermined location with respect to the near vision or bifocal lens region and a method for making the composite lens.
It is known in the eyeglass industry that plastic lenses can be molded in shapes to provide prescription lenses. These prescription lenses incorporate a corrective feature that alters light rays passing through the lenses. As used herein, the term "corrective feature" refers to an aspect of the lens that corrects for eyesight deficiencies. The term "optical center axis" is an imaginary line through the optical center of the lens which is normal or perpendicular to the lens. The optical center axis is the same as the main or principal axis of the lens.
Optical laboratories have been established which maintain a large quantity of plastic lenses having certain corrective features. Sometimes the lenses have to be ground and polished to match a prescription of a patient. At other times, the lab maintains a large stock of prescription lenses and the lenses are simply cut or edged and mounted in an eyeglass frame for the patient. The power of a lens is often times designated as a spherical power. Typical prescriptions for eyeglasses include +2.5, +1.25, +0.5, -0.75 and -3.00 and numerous other values. The plus sign in the spherical value designates a positive lenses. The negative sign designates a negative lens. In an eyeglass prescription, spherical value corrects for far or near vision deficiencies. The lab may maintain a stock of lenses that includes bifocal, multifocal or progressive vision lenses. These lenses correct for near vision deficiencies. Eyeglass prescriptions to correct for near vision deficiencies, such as bifocals, are designated ADD 1.25, ADD 2.25, ADD 3.00 and many other values. A number of patients can use this type of stock lenses without any grinding and polishing. However, a sizable percentage of the population requires lenses that correct for far vision, near vision and astigmatism. Astigmatism is corrected by using a cylinder lens that is rotated with respect to the horizontal to correct for the patient's astigmatism. The degree of the astigmatism varies from patient to patient and the lens must be carefully manufactured and positioned in the frame to correct for the astigmatism. Therefore, it is not practical for the optical lab to maintain stock lenses for typical corrective vision problems (far vision problems) as well as for the great variations of a astigmatism, and with near vision corrective lenses. Accordingly, it is customary in this industry to grind corrective lenses for astigmatic patients who require multifocal lenses. Eyeglass prescriptions to correct for astigmatism are designated with a spherical value, e.g. +1.50, a cylindrical value, e.g., -2.00 and an angular displacement off the horizontal that is called "the axis", e.g. 45.degree.. Accordingly, an astigmatic lens must have a power and an angle, for example -1.00 sph., -0.75 cyl. axis 100.degree..
If a person has near vision, far vision and astigmatic problems, the eyeglass prescription may be +2.50/-2.00 axis 110.degree. ADD +3.00.
U.S. Pat. No. 4,645,317 to Frieder, et al., discloses eyeglass lens modules and methods for making those modules. This patent discloses the use of plastic, corrective single vision stock lenses on which is glued a veneer overlay having a plus diopter bifocal or trifocal corrections. The veneer overlay must have a posterior curvature similar to the anterior curvature of the single vision stock lens which make the lens too thick. The veneer overlay is laminated or glued to the stock lens. However, Frieder, et al., do not disclose the use of two plastic lenses that cannot be used individually as corrective lenses because such lenses are too thin, do not disclose etching opposing surfaces of anterior and posterior plastic lenses, and do not disclose the use of heat to cause the lenses to return to their original shape after a deforming force is applied to the lenses. U.S. Pat. No. 4,690,512 to Forsyth discloses a composite lens assembly for two plastic lenses. Glue or optical cement is placed between the lenses in a gap of uniform width. Forsyth discloses the use of a primer comprising an aliphatic polyurethane. Forsyth states in the patent "While no explanation can be furnished for the superior results obtained by the use of the described priming layer on the surface 14 of the plastic lens element 10 as described, it is assumed that the lacquer applied to the surface of the plastic lens influences the molecular structure in such a manner that a firm and stable bond with the silicone adhesive used is established which as experience has shown does not occur in the absence of the primer". At column 3, lines 58-66. Forsyth does not disclose etching opposing services of the plastic lens nor using an adhesive or glue that has the same index of refraction as the posterior and anterior plastic lenses U.S. Pat. No. 3,877,798 to Tolar, et al., discloses a laminated multifocal lens. One of the lens is a bifocal or a multifocal lens and the other lens is a lens to correct for astigmatism. The lenses are glued together by an optical adhesive. Tolar, et al., do not disclose the step of etching surfaces of anterior and posterior lenses nor the use an adhesive that has an index of refraction equal to the index of refraction of the lenses. Tolar, et al., also do not disclose the use of heat to return the lenses to their original shape after the potentially deforming action of spreading the glue between the lenses. U.S. Pat. No. 3,711,417 to Schuler discloses plastic laminated lenses. However, these lenses are not etched prior to bonding together.
U.S. Pat. Nos. 3,620,888 to Buzzell; U.S. Pat. No. 3,588,216 to Bloom; U.S. Pat. No. 3,940,304 to Schuler; and, U.S. Pat. No. 4,679,918 to Ace disclose various composite lenses without disclosing etching of the lenses or heating of the lenses.
U.S. Pat. No. 4,522,768 to Roscrow discloses a casting gasket assembly and method for casting plastic lenses therefrom. The patent discloses a method and apparatus for casting plastic lenses. The disclosure of the Roscrow patent is incorporated herein by reference thereto.